Respiration and mitochondrial ATPase in energized mitochondria during isoproterenol-induced cell injury of myocardium

Effect of endotoxin, dobutamine and dopamine on muscle mitochondrial respiration in vitro

Introduction: Mitochondrial respiration is impaired during endotoxemia. While catecholamines are frequently used in sepsis, their effects on mitochondrial function are controversial. We assessed effects of dobutamine and dopamine endotoxin on isolated muscle mitochondria.

Materials and Methods : Sternocleidomastoid muscle mitochondria were isolated from six anesthetized pigs. Each sample was divided into six different groups. Three groups were incubated with endotoxin, three with vehicle. After 1 h, dopamine and dobutamine at final concentrations of 100 µM were added to the vehicle and endotoxin groups. After 2 h, state 3 and 4 respiration rates were determined for all mitochondrial complexes. Oxygen consumption was determined with a Clark-type electrode.

Results: Endotoxin increased glutamate-dependent state 4 respiration from 9.3 ± 3.6 to 31.9 ± 9.1 ( P = 0.001) without affecting state 3 respiration. This reduced the efficiency of mitochondrial respiration (RCR; state 3/state 4, 9.9 ± 1.9 versus 3.6 ± 0.6; P < 0.001). The other complexes were unaffected. Catecholamine partially restored the endotoxin-induced increase in complex I state 4 respiration rate (31.9 ± 9.1 versus 17.1 ± 6.4 and 20.1 ± 12.2) after dopamine and dobutamine, respectively ( P = 0.007), and enhanced the ADP:O ratio ( P = 0.033).

Conclusions: Dopamine and dobutamine enhanced the efficiency of mitochondrial respiration after short-term endotoxin exposure.

Impaired oxidative metabolism and calcium mishandling underlie cardiac dysfunction in a rat model of post-acute isoproterenol-induced cardiomyopathy

Stress-induced cardiomyopathy, triggered by acute catecholamine discharge, is a syndrome characterized by transient, apical ballooning linked to acute heart failure and ventricular arrhythmias. Rats receiving an acute isoproterenol (ISO) overdose (OV) suffer cardiac apex ischemia-reperfusion damage and arrhythmia, and then undergo cardiac remodeling and dysfunction. Nevertheless, the subcellular mechanisms underlying cardiac dysfunction after acute damage subsides are not thoroughly understood. To address this question, Wistar rats received a single ISO injection (67 mg/kg). We found in vivo moderate systolic and diastolic dysfunction at 2 wk post-ISO-OV; however, systolic dysfunction recovered after 4 wk, while diastolic dysfunction worsened. At 2 wk post-ISO-OV, cardiac function was assessed ex vivo, while mitochondrial oxidative metabolism and stress were assessed in vitro, and Ca(2+) handling in ventricular myocytes. These were complemented with sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA), phospholamban (PLB), and RyR2 expression studies. Ex vivo, basal mechanical performance index (MPI) and oxygen consumption rate (MVO2) were unchanged. Nevertheless, upon increase of metabolic demand, by β-adrenergic stimulation (1-100 nM ISO), the MPI versus MVO2 relation decreased and shifted to the right, suggesting MPI and mitochondrial energy production uncoupling. Mitochondria showed decreased oxidative metabolism, membrane fragility, and enhanced oxidative stress. Myocytes presented systolic and diastolic Ca(2+) mishandling, and blunted response to ISO (100 nM), and all these without apparent changes in SERCA, PLB, or RyR2 expression. We suggest that post-ISO-OV mitochondrial dysfunction may underlie decreased cardiac contractility, mainly by depletion of ATP needed for myofilaments and Ca(2+) transport by SERCA, while exacerbated oxidative stress may enhance diastolic RyR2 activity.

Protein kinase A catalytic subunit alters cardiac mitochondrial redox state and membrane potential via the formation of reactive oxygen species

BACKGROUND

The identification of protein kinase A (PKA) anchoring proteins on mitochondria implies a direct effect of PKA on mitochondrial function. However, little is known about the relationship between PKA and mitochondrial metabolism.

METHODS AND RESULTS

The effects of PKA on the mitochondrial redox state (flavin adenine dinucleotide (FAD)), mitochondrial membrane potential (DeltaPsi(m)) and reactive oxygen species (ROS) production were investigated in saponin-permeabilized rat cardiomyocytes. The PKA catalytic subunit (PKAcat; 50 unit/ml) increased FAD intensities by 56.6+/-7.9% (p<0.01), 2'7'-dichlorofluorescin diacetate (DCF) intensities by 10.5+/-3.3 fold (p<0.01) and depolarized DeltaPsi(m) to 48.1+/-9.5% of the control (p<0.01). Trolox (a ROS scavenger; 100 micromol/L) inhibited PKAcat-induced DeltaPsi(m), FAD and DCF alteration. PKAcat-induced DeltaPsi(m) depolarization was inhibited by an inhibitor of the inner membrane anion channel (IMAC), 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS: 1 micromol/L) but not by an inhibitor of mitochondrial permeability transition pore (mPTP), cyclosporine A (100 nmol/L).

CONCLUSIONS

PKAcat alters FAD and DeltaPsi(m) via mitochodrial ROS generation, and PKAcat-induced DeltaPsi(m) depolarization was not caused by mPTP but rather by DIDS-sensitive mechanisms, which could be caused by opening of the IMAC. The effects of PKA on mitochondrial function could be related to myocardial function under the condition of extensive beta-adrenergic stimulation.

Energetics of heart mitochondria during acute phase of Trypanosoma cruzi infection in rats

The energetics of heart mitochondria was studied in the acute phase of Trypanosoma cruzi infection in rats. Wistar rats were infected with 2 x 10(5) trypomastigote forms of the Y strain of T. cruzi, and heart mitochondria and submitochondrial particles isolated after 7 and 25 days of infection. Ultrastructure of mitochondria seemed to be preserved, but cytochrome c levels were significantly depressed. Respiratory control ratios (RCR) were decreased for glutamate and succinate oxidations, as a consequence of inhibition of respiration in state 3 and/or of stimulation of respiration in state 4. Stimulation of hydrolytic activity of FoF1-ATPase by energization of mitochondria was approx. 2-fold higher in relation to controls. Mitochondrial ATP concentration remained constant. In conclusion, during the acute phase of T. cruzi infection in rats there is an energy impairment at the level of heart mitochondria, but their ultrastructure and ATP concentration seem to be preserved; the maintenance of ATP may be due to an adaptative mechanism of the cell which includes inhibition of the hydrolytic activity of FoF1-ATPase.

Isoproterenol-dependent decrease in oxygen uptake and respiratory enzyme activities in rat myocardial tissue and mitochondria

OBJECTIVE

Myocardial damage induced by isoproterenol is believed to be secondary to increased oxygen demands on the heart. Our objective was to test an additional primary action of isoproterenol on tissue and mitochondrial oxidative metabolism and to compare these effects with the effects of other adrenergic agents in the presence of adrenergic inhibitors.

DESIGN

Prospective, dose-response study.

SETTING

Research laboratory at a university hospital.

SUBJECTS

Fifty Sprague-Dawley female rats (200 to 350 g), slightly anesthetized with ether and divided into several groups.

INTERVENTIONS

In 26 rats, the heart was removed, cut into fine slices (0.5-mm thickness), and placed in an ice-cold buffer. In 22 animals, the hearts were perfused in the Langendorff manner and chopped and processed for mitochondrial studies.

MEASUREMENTS AND MAIN RESULTS

We determined the following: a) the direct "in vitro" effects of isoproterenol and related catecholamines on normal oxygen uptake using myocardial slices; b) rat heart oxygen consumption and mitochondrial oxygen uptake from isolated organs, perfused with isoproterenol; c) measurements of enzyme activities in submitochondrial particles from the same perfused hearts; and d) the direct effects of isoproterenol on normal mitochondria isolated from normal nonperfused hearts. The oxygen uptake was determined polarographically with a Clark-type electrode and enzymatic activities were assayed by spectrophotometric reduction of cytochrome c at 550 nm with different mitochondrial substrates. Isoproterenol (0.01 to 100 nM) decreased the oxygen uptake by the heart slices in a dose-dependent manner. In comparison, epinephrine or norepinephrine per se did not change the parameter. However, with the addition of alpha-adrenergic receptor inhibitors, oxygen uptake decreased to values similar to those values obtained with isoproterenol. Also, mitochondria isolated from hearts perfused with isoproterenol had decreased state 3 respiratory rates (by 50%) and decreased respiratory control ratios (by 30%), without changes in adenosine 5'-diphosphate/oxygen ratios. The respiratory chain enzyme activities were also lowered.

CONCLUSIONS

The data suggest that while isoproterenol increases "in vivo" oxygen uptake by the working rat heart, isoproterenol can simultaneously decrease maximal adenosine 5'-diphosphate-induced mitochondrial oxygen uptake and in vitro myocardial tissue oxygen uptake, probably by modifying the mitochondrial respiratory enzymes. This action could be counteracted by alpha-adrenergic agonist effects.